1. Field of the Invention
This invention relates to stringers for slide fasteners and their methods of manufacture, and particularly to stringers employing molded thermoplastic coupling elements attached to polymer tapes.
2. Description of the Prior Art
The prior art as exemplified in U.S. Pat. No. 3,414,948, No. 3,490,111, No. 3,691,599 and No. 3,928,098 contains a number of slide fasteners having coupling elements attached to the edge of textile tapes. Some of the prior art such as is shown in the U.S. Pat. No. 3,928,098 disclose alternate U-shaped heel members of a filamentary stringer welded to opposite sides of a tape which is a woven or a nonwoven type with fibers. The textile tapes employed in the prior art provide support and maintain the spacing of coupling elements attached thereto. Tapes formed of polymer film having two laminated layers of highly oriented polymer wherein the orientations in the two layers are both oblique to the tape and transverse to each other have been previously proposed for use in slide fasteners; however these proposed slide fasteners utilize either (1) stitching to secure the elements to the polymer film tape which may be folded or (2) folded film tapes with continuous coupling elements inserted inside the fold with head portions protruding through slots extending transversely over the folded edge. Welding of coupling elements to such polymer tapes would generally result in inferior slide fasteners since the molecular orientation and increased strength along the direction of molecular orientations is deteriorated by the welding and the elements would easily be pulled from the tape by the forces on the slide fasteners.